1. Field of the Invention
The present invention is useful in bonding a low-energy plastic surface to metal such as, for example, in construction, automotive applications, fabricating, packaging, electrical insulation, and radiation shielding, etc. The adhesive composition described herein is effective in bonding a low-energy plastic surface to metal which provides an improved tensile lap shear strength when compared to the composition without silane containing the following components: (1) an ethylene-vinyl ester copolymer; (2) a tackifier selected from the following group: (a) a rosin, (b) a rosin ester, (c) a terpene resin, (d) a terpene-phenolic resin and (3) a rosin-modified phenolic resin; (3) a silane having the following structural formula: EQU R(CH.sub.2).sub.n [NH(CH.sub.2).sub.3 ].sub.m SiX.sub.3
wherein R is selected from the group consisting of amino, mercapto, glycidoxypropyl, epoxycyclohexyl, methacryloxy and vinyl; n is an integer from 0 to 6; m, when R is amino, is an integer from 0 to 1; m, when R is selected from the group consisting of mercapto, glycidoxypropyl, epoxycyclohexyl, methacryloxy and vinyl, is the integer 0; and X is selected from the group consisting of Cl, OCH.sub.3, OC.sub.2 H.sub.5 and OC.sub.2 H.sub.4 OCH.sub.3 ; and (4) a wax and a process for bonding said plastic surface to said metal.
2. Description of the Prior Art
Adhesive bonding of a low-energy plastic surface to metal by conventional adhesive bonding techniques, such as bonding polyethylene surfaces, requires some form of surface treatment prior to application of an adhesive to obtain high bond strengths between the surfaces so bonded. A low-energy plastic surface bonded to metal without prior surface treatment of either or both substrates by conventional methods known in the art results in either relatively weak bonds which are inadequate for many purposes such as those requiring strengths in a range in excess of several hundred or thousand pounds per square inch gauge of bonded area or would require the application of heat or pressure to form an effective bond.
Generally, for strong bonds involving a low-energy plastic surface and metal some form of surface treatment or etching of the low-energy plastic surface is required prior to application of an adhesive composition. Surface pretreatment of a low-energy plastic surface typically involves, for example, either acid etching with sulfuric, nitric, chromic acids or mixtures thereof, or flame treatment, corona discharge treatment or treatment with plasma jeta or low and high energy radiation, while the metal surface may also require some form of surface preparation such as acid etching or other form of cleaning or surface preparation.
Well known methods in the art for bonding a low-energy plastic surface to metal require surface treatment of the plastic or metal or both prior to bonding in a conventional adhesive process. These methods may further require post-clamping and long post-cure time. In other methods of bonding, heat and pressure are often utilized to exceed the softening point of the low-energy plastic surface, causing the adhesive composition to flow over the metal. In U.S. Pat. No. 3,192,092 a method for bonding a low-energy plastic surface to metal is described wherein adsorption of monomolecular layers of amphiphatic molecules between selected surfaces affords a bond between the surfaces.
Consequently, a need exists for an adhesive composition and much simpler process for bonding a low-energy plastic surface to metal. In accordance with the present invention a novel hot melt adhesive composition is provided which requires minimal heating of surfaces to be bonded and maximum bond strength in a matter of minutes or a few hours without resort to elaborate post-curing procedures. Further, the adhesive composition of the present invention can be applied in its melt form to a low-energy plastic surface and/or a metal in such a manner to provide rapid assembly of plastic surface-to-metal components and immediate handling of the assembled parts.
Applicant is unaware of any prior art relevant to the invention defined and claimed herein.